wingsandsword
Legend
But "space marine" predates any GW usage by quite a bit.
Earliest known appearance of the term "Space Marine" in science fiction literature was in November 1932, the short story "Captain Brink of the Space Marines" from Amazing Stories Magazine (Volume 7, Number 8). He also used the term again in the short story "The Space Marines and the Slavers" from 1939.
Robert Heinlein used the term in 1939 in his short story Misfit (and kept using it throughout his works).
Those are just the most prominent pre-WWII uses of the term.